Apple Chief Operations Officer Jeff Williams announced the study, which is being conducted in collaboration with Stanford University and with assistance from American Well, at Apple’s iOS 8 launch event in September.

“The most common form of serious arrhythmia is called atrial fibrillation or AFib, and it affects tens of millions of people and is a leading cause of stroke,” Williams said at the time. “But the challenge is, many people with AFib don’t feel symptoms, so it often goes undiagnosed. We’ve been looking at this for a couple years and we think Apple Watch can help. In our initial studies Apple Watch has been effective at surfacing irregular rhythms. So we’re expanding that work and today we’re announcing the Apple Heart Study.”

Anyone in the United States who has an Apple Watch Series 1 or later and is over the age of 21 is eligible to participate, and can do so by downloading a free app from the app store.

Participants in the study will have their heart rate continuously monitored. If the Apple Watch detects possible atrial fibrillation, the participant will see a notification on their Apple Watch and iPhone which will prompt them to commence a telemedicine consultation with a study doctor. American Well is providing the telemedicine services.

“The Apple Heart Study will advance the boundaries of clinical medicine significantly,” Ido Schoenberg, chairman and CEO of American Well, said in an emailed statement to MobiHealthNews. “This study is the first to bring connected care to clinical research, moving the cycle from the hospital to the home through a combination of wearables, analytics, telehealth and consumer devices. We see this as the beginning of a revolution that will save lives through early detection and more precise treatment, with applicability to many chronic conditions and millions of people.”

Assuming the participant doesn’t need urgent or emergency care, Stanford will ship an ECG monitoring patch (specifically BioTelemetry’s ePatch) to them. The user will wear the patch for a few days, allowing researchers to get side-by-side Apple Watch heart rate and ECG data.

“Through the Apple Heart Study, Stanford Medicine faculty will explore how technology like Apple Watch’s heart rate sensor can help usher in a new era of proactive health care central to our Precision Health approach,” Lloyd Minor, Dean of Stanford University School of Medicine, said in a statement. “We’re excited to work with Apple on this breakthrough heart study.”

This is the first ResearchKit study in which Apple itself has served as the sponsor, and signals that the company is becoming more and more hands-on with its health efforts. The company hopes to see enrollment on par with previous ResearchKit studies, which had upwards of 15 to 20,000 enrollees in the first week. In September Williams said that Apple worked closely with the FDA in developing the study.

Coincidentally, the news comes on the same day as the launch of AliveCor’s KardiaBand Apple Watch and SmartRhythm software, which actually have quite a bit in common with the Stanford study app. Both apps will monitor heart rate for signs of AFib and escalate to an ECG if necessary — but while the Apple study’s ECG will come in the mail, AliveCor’s is built right into the Watch strap.

AliveCor CEO Vic Gundotra told MobiHealthNews he doesn’t see Apple — who he praised as a helpful partner in bringing his device to market — as competition.

“No one has gotten FDA clearance outside of us for any ECG-related product,” he said. “Apple has announced they’re working with a PPG sensor, which I think everybody is, and that’s great. They announced their Stanford trial around PPG and that’s fine. We think the game-changer is going to be focused on the electrocardiogram.”

Another company long-focused on using PPG to detect atrial fibrillation is Cardiogram, which worked with UCSF last spring to publish data showing that, using a deep neural network, it could detect AFib from Apple Watch heart rate readings with 97 percent accuracy.

The potential benefits of tools and research like this are hard to overstate. Atrial fibrillation leads to 130,000 deaths and 750,000 hospitalizations in the US each year, partly because it’s often not accompanied by any symptoms. Apple is betting that more than a few of those deaths could be prevented if the arrhythmia is caught early— and that an always-on wearable like the Apple Watch might be the best chance at making that happen.